Method of molding a container

ABSTRACT

A method and molding system for hydraulic blow molding of a container from a preform. The method precharges the molding medium within a fill head unit to a precharge pressure. During the injecting of the molding medium into the preform, the method further increases the pressure of the molding medium to a pressure greater than the precharge pressure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national phase of PCT Application No.PCT/US2013/048477 filed on Jun. 28, 2013, the disclosure of which isincorporated in its entirety by reference herein.

BACKGROUND

The present invention generally relates to molding of plastic containersfrom preforms. More particularly, the invention relates to the formingof a plastic container from a preform utilizing a hydraulic blow moldingprocess.

Plastic containers are commonly used for the packaging of variousproducts, such as liquid products (including viscous liquids products).One common type of plastic container is the blow molded plasticcontainer, which is often formed of a polyester material, and morespecifically, polyethylene terephthalate (PET). Blow molded plasticcontainers are typically formed by placing a heated preform into a blowmold and then blowing and inflating the preform with air until thepreform contacts the interior surfaces of the mold cavity, which definethe final shape of the desired container. Once the inflated preform hasbeen held against the interior surfaces of the mold cavity by thepressure of the blow air for a length of time sufficient to “freeze” theplastic, the blow molded container is removed from the mold.

In traditional blow molding, after the heated preform has beenintroduced into the mold cavity, a stretch rod is often advanced withinthe preform to initiate longitudinal stretching of the preform beforeany significant radial expansion of the preform is undertaken by theintroduction of blow air. The stretch rod will may remain within thepreform during radial expansion and is retracted prior to removal of theresultant container from the molding machine.

The blow molded containers are then transported to the location wherethe containers will be filled with the intended product. This mayinclude the packaging and shipping of the containers to a remotelocation or may involve the transfer of the containers to a localfacility, where these final steps occur before being shipped to aretailer or end-user.

With the above method, blow molding and filling are distinct andseparate steps in the process of producing a product filled container. Anewer process involves the use of the actual end product in the moldingof the container. Instead of utilizing air as a blowing medium, this newprocess utilizes a liquid end product, the product being packaged in thecontainer and sold to the end consumer, as the container's moldingmedium. As used herein, this type of molding is referred to as hydraulicblow molding. In hydraulic blow molding, instead of air, the moldingmedium is the liquid that is intended to be packaged in the container.

Conventional blow molding, which uses air as a molding medium, utilizesa higher molding medium temperature than hydraulic blow molding.Generally, the temperature of the molding medium used in hydraulic blowmolding is in the range of only 10° C. to 100° C. Additionally, becauseof the liquid nature of the molding medium used in hydraulic blowmolding, heat is withdrawn preform at a rate that is faster than whenair is the molding medium. Thus, problems may arise in connection withthe axial stretching and radial expansion of the preform.

If the molding medium of hydraulic blow molding contacts the material ofthe preform prematurely, the molding medium can cause localized coolingof the material. This premature cooling can result in portions of thematerial insufficiently stretching and expanding and, therefore,insufficient and/or improper formation of the resulting container. Also,localized cooling of the material can cause the preform to blow-out, inthe area of such cooling, during the molding of the container.

Is it therefore important to minimize the extent to which the moldingmedium prematurely contacts the plastic of the preform. In other words,it is important to minimize the length of time that the product is incontact with the material of the preform before the preform has beenfully axially stretched and radially expanded into the finalconfiguration of the container.

During hydraulic blow molding, a chamber or bore of the nozzle is filledwith molding medium that has been delivered from a source at apredetermined system pressure. Once filled with the molding medium, aninlet valve closes thereby constraining the molding medium within thesystem. The system pressure of the molding medium at this point in inthe molding process is minimal, generally in the range of 1 to 2 bar.Next, the outlet of the nozzle is opened, the molding medium ispressurized so as to rapidly increase the pressure within the system andeject the molding medium from the nozzle's outlet into the preform,which is located within a mold assembly associated with the system.However, the raising of the pressure in the system is not instantaneous.The initial pressure driving the molding medium may not be sufficient toensure that the molding medium does not prematurely contact, or contactfor too long a length of time, the material of the preform. If suchcontact does occur, the result may be the blowing out of the preform oran improperly formed container.

If too much pressure is initially generated within the nozzle before thenozzle's outlet is opened, it is possible that some of the moldingmedium may breach the seal and drip into the preform. This too mayresult in a localized cooling of part of the preform and in animproperly formed container.

SUMMARY

In overcoming the enumerated drawbacks and other limitations of theknown technology, in one aspect the present invention provides a methodand system for hydraulic blow molding a container from a plasticpreform.

In another aspect, the invention provides, a method of operating amolding system 10 for hydraulic blow molding of a container 24 from apreform 18, the molding system including a fill head unit 12, the methodcomprising the steps of: providing a molding medium 42 in liquid formand at a system pressure to the fill head unit 12, injecting the moldingmedium 42 from the fill head unit 12 into the preform 18 causing thepreform 18 to expand into the shape of the container 24 under theinfluence of the molding medium 42, the method being characterized bythe steps of: precharging the molding medium 42 within the fill headunit 12 to a precharge pressure.

In a further aspect of the invention, during the step of injecting ofthe molding medium 42 into the preform 18, increasing the pressure ofthe molding medium to a pressure greater than the precharge pressure.

In an additional aspect of the invention, the molding medium 42 is heldat the precharge pressure.

In another aspect of the invention, an outlet 58 of the fill head unit12 is opened after the molding medium 42 has been held at the prechargepressure.

In yet a further aspect of the invention, the step of precharging themolding medium 42 is performed as a first part of a continuousincreasing of the pressure of the molding medium 42 from the fillpressure and during the step of injecting the molding medium 42 into thepreform 18.

In an additional aspect of the invention, the precharge pressure is atleast 3 bar.

In still another aspect of the invention, the precharge pressure is atleast 5 bar.

In a further aspect of the invention, an outlet 58 of the nozzle body 50is closed when the molding medium 42 is provided to the fill head unit12 and the outlet 58 is opened after precharging the molding medium 42to the precharge pressure.

In still an additional aspect of the invention, the outlet 58 is openedby retracting the seal pin 54 within the nozzle body 50.

In yet another aspect of the invention, a molding medium 42 is initiallyinjected into the preform 18 at the precharge pressure.

In a further aspect of the invention, subsequent to the injecting of themolding medium 42 into the preform 18 at the precharge pressure, themolding medium 42 is injected into the preform at a pressure greaterthan the precharge pressure.

In still an additional aspect of the invention, the pressurization unitincludes a fill piston 84 located within a fill chamber 82 containingthe molding medium 42, the fill piston 84 being moved to a prechargeposition during the precharging step.

In another aspect of the invention, the fill piston 84 is moved to theprecharge position by an actuator 86.

In still another aspect of the invention, the molding medium 42 isprovided to the fill head unit 12 at a system pressure and the prechargepressure is greater than the system pressure.

In another aspect of the invention provides for a hydraulic blow moldingof a container 25 from a preform 18, the molding system comprising afill head unit 12, the fill head unit 12 including a pressurization unit40 coupled to a nozzle assembly 38 and to a source 44 of molding medium42 in liquid form, the nozzle assembly 38 further including a nozzlebody 50 with a seal pin 54 slideably received within the nozzle body 50and being moveable between an opened position and a closed position, inthe closed position an outlet 58 of the nozzle body 50 being closed bythe seal pin 54, a mold assembly 14 having mold halves 16 defining amold cavity 22 in the shape of the container, the mold assembly 14 beingconfigured to receive the preform 18 therein; the molding system beingcharacterized by: a controller 96 coupled to the fill head unit 12, thecontroller 96 being configured to cause to raise the pressure of themolding medium 42 in the fill head unit 12 to a precharge pressure, thecontroller 96 being further configured to increase the pressure of themolding medium 42 above the precharge pressure during injection of themolding medium 42 into the preform 18.

In a further aspect of the invention, wherein the controller 96 isfurther configured to initiate injection of the molding medium 42 intothe preform 18 at the precharge pressure and subsequently raise thepressure of the molding medium 42 above the precharge pressure duringinjection of the molding medium 42 into the preform 18.

In an additional aspect of the invention, a pressurization unit 40coupled to the controller 96.

In another aspect of the invention, the pressurization unit 40 includesa fill piston 84 received within a fill chamber 82.

In a further aspect of the invention, the fill piston 84 is moveablebetween a retracted position and an extended position, the fill piston84 further having a precharge position located between the retractedposition and the extended position.

In an additional aspect of the invention, the controller 96 isconfigured to cause the fill piston 84 to be moved to and held at theprecharge position.

In another aspect of the invention, the fill piston 84 is coupled to anactuator 86 that moves the fill piston 84 between its retracted positionand extended position.

In yet a further aspect of the invention, the actuator 86 is a servomotor.

Further objects, features and advantages of this invention will becomereadily apparent to persons skilled in the art after a review of thefollowing description, with reference to the drawings and claims thatare appended to and form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is simplified, sectional view of a system, according to theprinciples of the present invention, for the hydraulic blow molding of acontainer;

FIG. 2 is a sectional view of the system seen in FIG. 1 at a subsequentstage of the hydraulic blow molding process;

FIG. 3 is a sectional view of the system seen in FIG. 1 at another stageof the hydraulic blow molding process according to the principles of thepresent invention;

FIG. 4 is a sectional view of the system seen in FIG. 1 at another stageof the hydraulic blow molding process;

FIG. 5 is a sectional view of the system seen in FIG. 1 at yet a furtherstage of the hydraulic blow molding process according to the presentinvention; and

FIG. 6 is a sectional view of the system seen in FIG. 1 at still anotherstage of the hydraulic blow molding process according to the principlesof the present invention.

DETAILED DESCRIPTION

Referring now to the drawings, illustrated in the figures is a hydraulicblow molding system, generally designated and referred to as moldingsystem 10, incorporating the principles of the present invention. As itsprimary components, the molding system 10 includes a fill head unit 12and a mold assembly 14. As mentioned above, hydraulic blow molding usesa liquid as the molding medium. As the term is used herein, liquid isintended to include not only those liquids with a viscosity near water(e.g. beverages and non-beverages, including water, sports drinks, tea,etc.), but also those liquids with a viscosity substantially greaterthan water and generally referred to as viscous liquids (e.g. condimentsand household products, including ketchup, dishwashing liquid, etc.).

The mold assembly 14 associated with the molding system 10 generallyincludes a pair of mold halves 16 that are hinged or otherwise connectedso as to open and close, thereby allowing a preform 18 to be receivedtherein. The mold halves 16 each having interior surfaces 20 thatcooperate to define a mold cavity 22, which itself defines the shape ofthe container 24 (seen in FIGS. 4-6) formed by the molding system 10.

The preform 18 generally includes an elongated tubular body 26 that isbounded by and extends between a closed end 28 and an open end 30.Adjacent to the open end 30 are a finish 32, which may be threaded, anda handling ring 34, which respectively receive a closure cap (not shown)and assist in the handling of the preform 18 and resultant container 24.

The fill head unit 12 is generally comprised of a housing 36, a nozzleassembly 38, and a pressurization means or pressurization unit 40. Themolding medium 42, which is also the end product that is being packagedwithin the container 24, is provided to the pressurization unit 40 froma source 44 and from the pressurization unit 40 through the housing 36to the nozzle assembly 38. The nozzle assembly 38 will in turn directthe molding medium 42 into the preform 18 causing the preform to beaxially stretched and radially expanded into conformity with theinterior surfaces 20 defining the cavity 22.

As seen in FIG. 1, the nozzle assembly 38 is movably received within thehousing 36. To receive the nozzle assembly 38, a bore 48 is definedlongitudinally within the housing 36. The nozzle assembly 38 is furtherdefined by a nozzle body 50 having portions defining a main bore 52within which a seal pin 54 is slideably received. To effectuate movementof the seal pin 54, the seal pin 54 is coupled to an actuator 56. Theactuator 56 may be any one of a well-known variety of actuators and maycause movement of the seal pin 54 by way of mechanical,electromechanical, servo, pneumatic, hydraulic or other actuation means.

Defined within the nozzle body 50, and more particularly within the mainbore 52, are one or more inlets 56 and an outlet 58. The inlets 56transverse the wall of the nozzle body 50 and may be equidistant spacedabout a portion of the nozzle body 50 as is further described below. Theoutlet 58 is defined at the distal end 60 of the nozzle body 50 anddefines the exit orifice from which the molding medium 42 is ejectedinto the preform 18. Also defined in the distal end 60 of the nozzlebody 50 is a frustoconical surface that operates as a valve seat 62 andinteracts with the seal pin 54 to seal and close off the outlet 58during various stages of operation of the fill head unit 12.

The seal pin 54, as noted previously, is slidable within the main bore52 of the nozzle body 50. This sliding movement operates to translatethe seal pin 54 between a closed position and an opened position. In theclosed position, which is seen in FIG. 1, a distal end 64 of the sealpin 54 sealingly engages the valve seat 62 to close the outlet 58. Morespecifically, a sealing surface 66, which has a correspondingfrustoconical shape, contacts the valve seat 62 to form a sealedengagement. In its opened position, the seal pin 54 is retracted by theactuator 56 such that the sealing surface 66 is spaced apart from thevalve seat 62, thereby opening the outlet 58 of the nozzle assembly 38and allowing the molding medium 42 to flow therethrough into the preform18. The open position of the seal pin 54 is generally shown in FIG. 4.

Provided in a central bore 68 of the seal pin 54 is a stretch rod 70.The stretch rod 70 extends through the seal pin 54 and is movablebetween a retracted position and an extended position by an actuator 71.This actuator 71 may be of the same or different variety than theactuator 56 utilized in the displacing of the seal pin 54. In itsretracted position, a tip 74 of the stretch rod 70 may be withdrawn intothe distal end 60 of the seal pin 54 or located adjacent thereto. In itsextended position, the stretch rod 70 is advanced such that the tip 74extends into the body 26 of the preform 18. As further discussed below,axial stretching of the preform 18 is caused by engagement of the tip 74with the closed end 28 of the preform 18, and subsequent advancement ofthe stretch rod 70.

The pressurization unit 40 provides the molding medium 42 to the nozzleassembly 38 through a discharge port 76 formed in the wall of thehousing 46. In the area of the discharge port 76, portions along theexterior surface of the nozzle body 50 define a circumferential recess78 that operates as receiving space 79 for receipt of the molding medium42 from the discharge port 76. Opening into this receiving space 79 arethe inlets 56 of the main bore 52, which therefore allow for the flow ofthe molding medium 42 into the main bore 52.

The pressurization unit 40 maybe any means by which the molding medium42 can be pressurized during the molding. As such, the pressurizationunit 40 may be a high-pressure pump, a piston and cylinder arrangement,or any other mechanism/arrangement that will allow the pressure of themolding medium 42 to be increased to a pressure suitable for molding ofthe container 24. As illustrated in the various figures, thepressurization unit 40 is a piston and cylinder arrangement. In thisarrangement, a cylinder 80 defines a fill chamber 82 within which a fillpiston 84 is reciprocally positioned. The fill piston 84 is coupled toan actuator 86, which may be any of the previously mentioned types ofactuator, but it is preferably a servo motor. The fill piston 84 isaccordingly movable between a retracted position, seen in FIG. 1, and anextended position, which is seen in FIG. 4.

To allow for the flow of the molding medium 42 into the fill chamber 82,the fill port 88 is defined in the wall of the cylinder 80. The fillport 88 is coupled by way of a feed line 90 to the source 44 of themolding medium 42, and an inlet valve 92, associated with the fill port88, is movable by another actuator 94 so as to close off or keep openthe feed line 90 during certain stages of operation of the moldingsystem 10.

During operation, the molding system 10 begins a molding cycle with thenozzle assembly 38 retracted by its actuator 39 and disengaged from apreform 18 that has been positioned in the mold assembly 14 such thatthe body 26 of the preform 18 extends into the cavity 22 defined by themold halves 16. Additionally, the seal pin 54 is in its closed positionand the sealing surface 66 engage the valve seat 62 to close the outlet58 and the main bore 52. The molding medium 42 is then provided from thesource 44 and received in the fill chamber 82 through the fill port 76.Since the only constriction on the flowing of the molding medium 42 isthe engagement of the sealing surface 66 with the valve seat 62, themolding medium 42 flows through the discharge port 76 and into thereceiving space 79 defined by the recess 78. Since the inlets 56 are incommunication with the receiving space 79, the molding medium 42 alsoflows through the inlets 56 and into the main bore 52 of the nozzle body50.

This flow of the molding medium 42 into the fill chamber 82 is such thatthe fill chamber 82 becomes substantially completely or completelyfilled with the molding medium 42, as is the receiving space 79 and themain bore 52 defined in the nozzle body 50.

Once the various cavities, spaces and bores have been filled with themolding medium 42, the inlet valve 92 is closed, constraining themolding medium 42 therein. Generally around the time that the inletvalve 92 is closed, the nozzle body 50 and seal pin 54 are advancedtogether such that the distal end 60 of the nozzle body 50 engages theupper surfaces of the preform 18 and/or the upper surfaces of the moldassembly 14. The engagement of the nozzle body 50 with the uppersurfaces of the preform 18 forms a fluid tight seal therebetween. Alsoaround this time, the stretch rod 70 is advanced to the point where thetip 74 of the stretch rod 70 engages the closed-end 28 of the preform18. The above is seen in FIG. 2.

While the molding material 42 is being constrained in the molding system10, or prior that constraining but after engagement of the nozzle body50 with the upper surface of the preform 18, the stretch rod 70 isadvanced to axially stretch the preform 18. This is illustrated in FIG.3. The stretch rod 70 may then be retracted to a position where the tip74 of the stretch rod 70 is flush with, adjacent to or slightly recededwithin the distal end 64 of the seal pin 54.

As also seen in FIG. 3, while the seal pin 54 is still engaged with thenozzle body 50 at their distal ends 60, 64 and after the inlet valve 92has been closed, the fill piston 84 is partially advanced by itsassociated actuator 86 to a precharge position. This partial advancementof the fill piston 84 within the cylinder 80 operates to precharge themolding medium 42 constrained within fill head unit 12 of the moldingsystem 10. The advancement of the fill piston 84 is such that systempressure of the molding medium 42 within in the fill head unit 12 israised to a precharge pressure of at least 3 bar, and more preferably atleast 5 bar. Precharging the molding medium 42 to the precharge pressuredrives the molding medium 42 into the preform 18, upon opening of theseal pin 54, with sufficient initial acceleration and velocity that themolding medium 42 does not contact the material of the preform 18 fortoo long a length of time before the container 24 is fully formed. Inother words, premature contact of the molding medium 42 with thematerial of the preform 18 does not occur. Precharging below theseprecharge pressures produces inconsistent molding results of the typepreviously discussed.

After the fill head unit 12 has been precharged, the seal pin 54 ismoved to its open position, opening the outlet 58, and the fill piston84 is driven to its extended position, as seen in FIG. 4. As a result,the molding medium 42 is caused to flow from the fill chamber 82,through the receiving space 79, into the main bore 52, and be injectedinto the preform 18. Upon opening of the outlet 58, the pressure in themolding system 10 initially drops, but quickly recovers and increases tothe precharge pressure, and thereafter rises above the prechargepressure. The accompanying flow of the molding medium 42 causes thepreform 18 to expand into conformity with the interior surfaces 20 andinto the desired shape. Thus, the precharging of the molding medium 42increases the initial acceleration experienced by the molding medium 42when the outlet 58 is opened, as compared to a system withoutprecharging. This in turn decreases the overall amount time that themolding medium 42 is in contact with the material of the preform 18before the preform 18 has been fully expanded into the shape of thecontainer 24 as a result of the fill piston 84 being driven to itsextended position. Thus, the amount of heat that can be removed from thepreform 18 before it is fully formed into the container is reduced.

The precharge position of the fill piston 84 and the precharging of themolding medium 42 can be achieved in at least two ways. According to onemethod, the fill piston 84 is moved to the precharge position seen inFIG. 3 and stopped and held at this position. Thereafter, the seal pin54 is moved to its open position in the fill piston 84 is moved from theprecharge position to its extended position. According to another methodof operation, the fill piston 84 is not stopped and held at theprecharge position. Rather, the fill piston 84 is moved from itsretracted position (seen in FIG. 2) and the movement of the seal pin 54to its opened position is timed such that this movement of the seal pin54 occurs when the fill piston 84 has reached the precharge position(seen in FIG. 3) and/or the molding medium 42 has reached the prechargepressure. Thus, the precharging of the molding medium 42 is performed asa first part of a continuous increasing of the pressure of the moldingmedium 42 from the system pressure during the injection of the moldingmedium 42 into the preform.

Control of the timing of the opening of the seal pin 54 can also beachieved in several ways. Firstly, retraction of the seal pin 54 can becontrolled based on an elapsed time after initiation of the extending ofthe fill piston 84, which may be determined by an internal clock of acontroller 96 associated with the molding system 10. (The controller 96is illustrated in FIG. 1, but omitted from the remaining figures forclarity purposes.) Secondly, retraction of the seal pin 54 can becontrolled based upon the fill piston 84 being extended a predeterminedlength or reaching a predetermined position, which may be determined byposition sensors associated with the fill piston 84. Thirdly, retractionof the seal pin 54 can be initiated upon the reaching of a predeterminedprecharge pressure within the fill chamber 82, which may be determinedby the pressure sensors coupled to the fill chamber 82.

Once the container 24 has been formed by and filled with the moldingmedium 42, the seal pin 54 is again moved to its closed position, whichis seen in FIG. 5. Prior to the closing of the outlet 58 by the seal pin54, the stretch rod 70 may be extended into the finish 32 of thecontainer 24 and the molding medium 42 in order to set the final fillheight of the molding medium 42 in the container 24.

Upon disengagement of the nozzle assembly 38 from the container 24 andmold assembly 14, and upon withdrawal of the stretch rod 70 from themolding medium 42, the fill height of the molding medium 42 will loweror drop by an amount equal to the volume of liquid that was beingdisplaced by the stretch rod 70. The container 24 filled with themolding medium 42, which is the desired end product, may then be removedfrom the mold assembly 14. With the seal pin 54 in its closed position,the inlet valve 92 may be opened and the fill piston 84 moved to itsretracted position, thereby allowing the fill chamber 82 to refill withthe molding medium 42 from the source 44. At this point, the process orcycle of the molding system 10 is repeated to form and fill anothercontainer 24.

As a person skilled in the art will readily appreciate, the abovedescription is meant as an illustration of implementation of theprinciples this invention. This description is not intended to limit thescope or application of this invention in that the invention issusceptible to modification, variation and change, without departingfrom spirit of this invention, as defined in the following claims.

We claim:
 1. A method of operating a molding system for hydraulic blowmolding of a container from a preform, the molding system including afill head unit, the method comprising the steps of: providing a moldingmedium in liquid form and at a system pressure to the fill head unit,injecting the molding medium from the fill head unit into the preformcausing the preform to expand into the shape of the container under theinfluence of the molding medium; and precharging the molding mediumwithin the fill head unit to a precharge pressure, the precharging ofthe molding medium being performed as a first part of a continuousincreasing of the pressure of the molding medium from the fill pressureand during the injecting of the molding medium into the preform.
 2. Themethod of claim 1, further comprising that, during the step of injectingof the molding medium into the preform, increasing the pressure of themolding medium to a pressure greater than the precharge pressure.
 3. Themethod of claim 1, further comprising the step holding the moldingmedium at the precharge pressure.
 4. The method of claim 3, wherein anoutlet of the fill head unit is opened after the molding medium has beenheld at the precharge pressure.
 5. The method of claim 1, wherein theprecharge pressure is at least 3 bar.
 6. The method of claim 1, whereinthe precharge pressure is at least 5 bar.
 7. The method of claim 1,wherein an outlet of the nozzle body is closed when the molding mediumis provided to the fill head unit and the outlet is opened afterprecharging the molding medium to the precharge pressure.
 8. The methodof claim 7, wherein the outlet is opened by retracting the seal pinwithin the nozzle body.
 9. The method of claim 1, wherein molding mediumis initially injected into the preform at the precharge pressure. 10.The method of claim 9, wherein subsequent to the injecting of themolding medium into the preform at the precharge pressure, the moldingmedium is injected into the preform at a pressure greater than theprecharge pressure.
 11. The method of claim 1, wherein thepressurization unit includes a fill piston located within a fill chambercontaining the molding medium, the fill piston being moved to aprecharge position during the precharging step.
 12. The method of claim11, wherein the fill piston is moved to the precharge position by anactuator.
 13. The method of claim 1, wherein the molding medium isprovided to the fill head unit at a system pressure and the prechargepressure is greater than the system pressure.
 14. A molding system forhydraulic blow molding of a container from a preform, the molding systemcomprising a fill head unit, the fill head unit including apressurization unit coupled to a nozzle assembly and to a source ofmolding medium in liquid form, the nozzle assembly further including anozzle body with a seal pin slideably received within the nozzle bodyand being moveable between an opened position and a closed position, inthe closed position an outlet of the nozzle body being closed by theseal pin, a mold assembly having mold halves defining a mold cavity inthe shape of the container, the mold assembly being configured toreceive the preform therein; the molding system being characterized by:a controller coupled to the fill head unit, the controller beingconfigured to raise the pressure of the molding medium in the fill headunit to a precharge pressure, the controller being further configured tocontinuously increase the pressure of the molding medium in the fillhead unit to and above the precharge pressure during injection of themolding medium into the preform.
 15. The molding system of claim 14,wherein the controller is further configured to initiate injection ofthe molding medium into the preform at the precharge pressure andsubsequently raise the pressure of the molding medium above theprecharge pressure during injection of the molding medium into thepreform.
 16. The molding system of claim 14, further comprising apressurization unit coupled to the controller.
 17. The molding system ofclaim 16, wherein the pressurization unit includes a fill pistonreceived within a fill chamber.
 18. The molding system of claim 17,wherein the fill piston is moveable between a retracted position and anextended position, the fill piston further having a precharge positionlocated between the retracted position and the extended position. 19.The molding system of claim 17, wherein the controller is configured tocause the fill piston to be moved to and held at the precharge position.20. The molding system of claim 17, wherein the fill piston is coupledto an actuator that moves the fill piston between its retracted positionand extended position.
 21. The molding system of claim 20, wherein theactuator is a servo motor.